World 6-1 (New Super Mario Bros.)
From the Super Mario Wiki
This level is filled with Bullet Bills that are fired from Bill Blaster Turrets. When Mario reaches a thin ledge, he can either hang onto it or walk on it. When Mario is on the thin ledge, it is harder for him to jump than usual. If Mario Wall Jumps on the wall after the thin ledge, he will be able to get the first Star Coin. After the midway point, Mario should jump to the left to get the second Star Coin. Below another thin ledge, after many Bullet Bills, is the final Star Coin. After the third Star Coin, Mario will reach the flagpole.